1. Field of Invention
The invention relates to wireless communications, and more specifically to a wireless communication device that is capable of transmitting emergency signals to a wireless receiver even when the wireless communication device is outside of a coverage zone of the wireless receiver.
2. Related Art
Wireless communication devices, such as cellular telephones to provide an example, are becoming commonplace in both personal and commercial settings. The wireless communication devices provide users with access to all kinds of information. For example, a user can access the internet through an internet browser on the device, download miniature applications (e.g., “apps”) from a digital marketplace, send and receive emails, or make telephone calls using a voice over internet protocol (VoIP). Consequently, wireless communication devices provide users with significant mobility, while allowing them to remain “connected” to communication channels and information.
Wireless communication devices communicate with one or more other wireless communication devices or wireless access points to send and receive data. Typically, a first wireless communication device generates and transmits a radio frequency modulated with encoded information. This radio frequency is transmitted into a wireless environment and is received by a second wireless communication device. The second wireless communication device demodulates and decodes the received signal to obtain the information. The second wireless communication device may then respond in a similar manner. The wireless communication devices can communicate with each other or with access points using any well-known modulation scheme, including amplitude modulation (AM), frequency modulation (FM), quadrature amplitude modulation (QAM), phase shift keying (PSK), quadrature phase shift keying (QPSK), and/or orthogonal frequency-division multiplexing, as well as any other communication scheme that is now, or will be, known.
Typical modulation schemes also include a standard or minimum coding rate used for forward error correction (FEC). The coding rate defines the number of redundant error-check bits used for each bit of non-redundant information. FEC increases the probability that transmitted information will be successfully received (error free). Low coding rates provide a greater likelihood of successful transmission, but require more energy to transmit the encoded information due to the larger number of bits associated with the information. Conversely, higher coding rates require less energy, but decrease the likelihood of successful transmission due to a smaller number of error-check bits.
Regardless of the coding rate employed, the ability of the wireless communication device to successfully transmit/receive data is typically limited by the range of coverage of the wireless access points. For example, a wireless network, such as a cellular network to provide an example, contains a plurality of access points in the form of base stations that each define a coverage cell. Each cell defines the coverage zone for a corresponding base station, and is based on a modulation scheme used in the wireless network and the modulation scheme's corresponding standard/minimum coding rate. Wireless communication devices within the cell communicate with the base station to send and receive data. If the wireless communication device moves from one cell to another, various methods exist to pass communication responsibilities from the base station of the original cell to a base station associated with the new cell. However, if the wireless communication device exits the coverage zone (i.e., is not within any cell), the wireless communication device will be incapable of sending/receiving data using the modulation scheme and standard/minimum coding rate designated for use within the wireless network. Consequently, the wireless communication device “loses service” and the ability to communicate with the cellular network.
Loss of service typically occurs in rural areas due to lack of cellular towers (base stations), and within certain structures due to high path loss, noise, or interference. Although this loss of service often amounts to a mere nuisance, the inability to communicate with the network can prove life-threatening in emergency situations because a user will be unable to request assistance or even notify emergency services of his location. A similar danger may arise when a power supply (i.e., a battery) of the wireless communication device has insufficient power to operate the device in a normal condition, or to modulate and encode the necessary data using the designated modulation scheme and coding rate.
Thus, there is a need for a wireless communication device that can effectively communicate emergency data to a wireless access point even when the wireless communication device is outside of the wireless network or lacks sufficient battery power to communicate with the network using the designated modulation and coding scheme. Further aspects and advantages of the invention will become apparent from the detailed description that follows.
The invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an element first appears is indicated by the leftmost digit(s) in the reference number.